【USACO 2011】 道路和航线

【题目链接】

              点击打开链接

【算法】

           SPFA + SLF / LLL 优化

【代码】

           

#include<bits/stdc++.h>
using namespace std;
#define MAXT 25000

int i,T,R,P,S,u,v,w;
int dist[MAXT+10],vis[MAXT+10];
vector<pair<int,int> > E[MAXT+10];

template <typename T> void read(T &x) {
        int f=1; char c = getchar(); x=0;
        for (; !isdigit(c); c = getchar()) { if (c=='-') f=-1; }
        for (; isdigit(c); c = getchar()) x=x*10+c-'0';
        x*=f;
}

inline void SPFA() {
        int i,x,to,cost;
        deque<int> q;
        for (i = 1; i <= T; i++) dist[i] = 2e9;
        dist[S] = 0; 
        q.push_back(S);
        while (!q.empty()) {
                x = q.front(); q.pop_front();
                vis[x] = 0;
                for (i = 0; i < E[x].size(); i++) {
                        to = E[x][i].first;
                        cost = E[x][i].second;
                        if (dist[x] + cost < dist[to]) {
                                dist[to] = dist[x] + cost;
                                if (!vis[to]) {
                                        vis[to] = 1;
                                        if ((q.empty()) || (dist[to] > dist[q.front()])) q.push_back(to);
                                        else q.push_front(to);
                                }
                        }
                } 
        }
}

int main() {
        
        read(T); read(R); read(P); read(S);
        
        for (i = 1; i <= R; i++) {
                read(u); read(v); read(w);
                E[u].push_back(make_pair(v,w));
                E[v].push_back(make_pair(u,w));    
        } 
        for (i = 1; i <= P; i++) {
                read(u); read(v); read(w);
                E[u].push_back(make_pair(v,w));    
        }
        
        SPFA();
        
        for (i = 1; i <= T; i++) {
                if (dist[i] == 2e9)
                        cout<< "NO PATH" << endl;
                else cout<< dist[i] << endl;
        }
        
        return 0;
    
}